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previous: Trace Bruce;My curiousity... -- 7/22/1999 1:59 AM

Re: Holy Cow! Have you seen London Power?

7/22/1999 9:15 AM
Niek	Re: Holy Cow! Have you seen London Power? Hi As far as I know, the only (easy) way to regulate AC voltage is using a variac. Mr. O'Connor might be using a variac that is directly mains connected (primary) and has a variable AC output secondary. This is rectified and filtered and used for the power amp supply. On the side he has an ordinary valve power transformer for heaters and preamp B+ supply. I am only wondering how it works with the biasing, you'd have to change this if you bring the power amp supply up or down. You could use a tap on the ordinary transformer for a set DC bias supply level and add to that a small DC voltage from the high voltage supply so you have a varying bias control within certain limits. With cathode bias you could probably avoid this, I don't think the power amp B+ is regulated below, say 50 V DC. Anybody tried a switch-mode power supply for varying B+ ? Seems quite sensible if you address the noise problems properly. My lab HV lab supply is switched mode and variable and works like a charm with valve equipment. You can get away with a really small transformer and get lots of oomph. Hang on, did Mr. O'Connor maybe opt for this ? It is after all some kind of AC regulation. Niek

7/22/1999 9:15 AM

Niek

Re: Holy Cow! Have you seen London Power?

Hi

As far as I know, the only (easy) way to regulate AC voltage is using a variac. Mr. O'Connor might be using a variac that is directly mains connected (primary) and has a variable AC output secondary. This is rectified and filtered and used for the power amp supply.

On the side he has an ordinary valve power transformer for heaters and preamp B+ supply. I am only wondering how it works with the biasing, you'd have to change this if you bring the power amp supply up or down. You could use a tap on the ordinary transformer for a set DC bias supply level and add to that a small DC voltage from the high voltage supply so you have a varying bias control within certain limits. With cathode bias you could probably avoid this, I don't think the power amp B+ is regulated below, say 50 V DC.

Anybody tried a switch-mode power supply for varying B+ ? Seems quite sensible if you address the noise problems properly. My lab HV lab supply is switched mode and variable and works like a charm with valve equipment. You can get away with a really small transformer and get lots of oomph.

Hang on, did Mr. O'Connor maybe opt for this ? It is after all some kind of AC regulation.

Niek

Replies:

Ken g OK,Judging by what ... -- 7/22/1999 12:55 PM